fix(mixins): merge unmounted and beforeUnmount options

[laineus]

Issue

unmounted and beforeUnmounted options will not be merged and never be called.

Demo

Codepen: https://codepen.io/laineus/pen/qBjEggq

<template>
  <ul id="app">
    <li>created: {{ $options.created }}</li><!-- ⭕Array -->
    <li>mounted: {{ $options.mounted }}</li><!-- ⭕Array -->
    <li>unmounted: {{ $options.unmounted }}</li><!-- ❌Function -->
    <li>beforeUnmounted: {{ $options.beforeUnmounted }}</li><!-- ❌Function -->
  </ul>
</template>

<script>
export default {
  created () {},
  mounted () {},
  unmounted () {},
  beforeUnmounted () {},
  mixins: [
    {
      created () {},
      mounted () {},
      unmounted () {}, // Will not be called
      beforeUnmounted () {} // Will not be called
    }
  ]
}
</script>

Version

v3.1.0-beta.7 to latest (v3.2.6) -> happens
v3.1.0-beta.6 or lower -> ok

related commit: e2ca67b#diff-bef066f3036cebd9b6db8a01d40f6eb0fdfe71c06da414b7d226652c016d7efdR982

It seems just forgotten to add global merge strategies for unmounted and beforeUnmounted.

[posva]

Can you add tests?

[laineus]

@posva
I have added one case into existing test. 88ecea9
It will not be passed on master, and will be passed on this PR.

I figured it's not need cases for all options, so I didn't.

[posva]

beforeUnmount should be added too

[laineus]

@posva I have added for beforeUnmount too.
It passed properly on my local.

Could you check it again?